Distributed energy resource units, like solar cells or wind turbines, connected to a common electricity network provide in this electricity network islands (i.e., parts of the common electricity network, which are provided with power generation of their own). A single-phase islanding condition is a partial loss-of-mains situation in which a single phase of an electricity network incorporating power generation loses connection with the rest of the common electricity network. It is important to detect a single-phase islanding condition since it causes a safety hazard within the electricity network being partially separated from the common electricity network.
There are several known methods for single-phase islanding detection in a three-phase electricity network. A known method for single-phase islanding detection involves adding a low frequency stimulus reference signal into a reactive current reference of a frequency converter supplying the electricity network, and comparing a rate of change of network frequency with a normal value of the rate of change, wherein a single-phase islanding condition increases the rate of change of network frequency.
Known methods for single-phase islanding detection increase harmonic distortion in the electricity network and/or detect a single-phase islanding condition slowly.